PFM switching regulators generally include a reference voltage source, a comparator circuit, a PFM control circuit, p-channel MOSFET (PMOS) switch, n-channel MOSFET (NMOS) switch, an input voltage source, a LC circuit with an off-chip Inductor and an off-chip capacitor. The output voltage of the PFM switching regulator is coupled to a load. The output voltage of the PFM switching regulator is compared with the reference voltage by the comparator circuit to generate a control signal to the PFM control circuit. Based on the control signal, the PFM control circuit selectively turns on PMOS switch or NMOS switch to maintain a near constant output voltage, in addition to supplying the load current.
As one skilled in the art appreciates the selective switching of the PMOS switch or NMOS switch generates a ripple on the output voltage. The ripple on the output voltage is about twice the hysteresis of the comparator circuit.